It is often defined to encompass the historic counties of Cornwall, Devon, Dorset and Somerset and the City of Bristol, while the counties of Gloucestershire and Wiltshire are also often included.

Some usages of the term include even wider areas, while others are more specific though with little consistency of definition.

It is increasingly used – e.g. by the West of England Partnership – as a synonym for the former Avon (county) area.

Wessex Regionalists seek to promote this as an alternative to the South-West region, including some counties in central southern England – Hampshire, Berkshire, Oxfordshire and the Isle of Wight – and excluding Devon and Cornwall which equate to historic Brythonic kingdom of Dumnonia.